1. Field of the Invention
The present invention relates to a phase shift circuit capable of significantly decreasing an electromagnetic interference (EMI) component of an input/output signal by adjusting a phase difference between driving signals of switches operating a main circuit and a sub-circuit included in a power factor correction circuit, and a power factor correction circuit including the same.
2. Description of the Related Art
Recently, in the electrical appliance and electronic device fields, research into a method of removing harmonic components generated in an input terminal of an electronic apparatus in order to significantly decrease an effect on a power line of an electrical appliance or electronic device and reduce interference with other appliances and devices has been actively undertaken. As an efficient method of removing harmonic components, a power factor correction (PFC) circuit may be used. A power factor correction circuit may be classified as a passive-type power factor correction circuit or an active-type power factor correction circuit, according to whether or not it includes a switch. The passive-type power factor correction circuit has disadvantages in that a form factor thereof may be large, and an effect thereof may not be great. Therefore, recently, active-type power factor correction circuits have been widely used.
Among active-type power factor correction circuits, an interleaving-type power factor correction circuit using at least two identical power factor correction circuits connected to each other in parallel has characteristics that depend on a phase difference between signals for operating a plurality of circuits connected to each other in parallel. For example, when it is assumed that two identical power factor correction circuits are connected to each other in parallel in a master-slave scheme, in the case in which driving signals for operating switches respectively included in the two identical power factor correction circuits have a phase difference of 180 degrees therebetween, an electromagnetic interference (EMI) component of an input/output signal may be significantly decreased. When the phase difference between the driving signals for a main circuit and a sub-circuit deviates from 180 degrees, a ripple component of an input current increases, such that an EMI component increases.
In the interleaving-type power factor correction circuit, various type phase shift circuits have been suggested in order to maintain a phase difference between switching devices included in respective circuits at a required value. However, in the phase shift circuit suggested in the related art, a selection condition in selecting a current source included in the circuit was limited or it was difficult to accurately generate a required phase difference.
In the following Related Art Documents, Patent Document 1, which relates to an interleaved-type switching converter, and an apparatus and method of controlling the same, discloses a method of switching power in an interleaving scheme to generate a control signal and maintaining a phase difference at a required value, for example, 180 degrees. Patent Document 2, which relates to a phase shift and synchronization circuit, discloses a feature of adjusting a sink between control signals of the respective switching devices in an interleaving-type power factor correction circuit. However, neither Patent Document 1 nor Patent Document 2 discloses a feature of changing a polarity of a voltage of a capacitor in a circuit controlling a phase difference to operate a switch at a required phase difference.